Electrical lead

ABSTRACT

An electrically conductive member includes an elongate body, which has at least one electrically conductive region. The electrically conductive region comprises a porous polymeric material coated with an electrically conductive material. A method of manufacturing the electrically conductive member includes the steps of extruding an elongate body of polymeric material, wherein at least one region of the elongate body is porous in nature; and coating the elongate body with an electrically conductive material, such that the electrically conductive material substantially coats the pores of the at least one region.

This application is a continuation application under 35 U.S.C. §120 ofU.S. Pat. application Ser. No. 11/123,392, filed May 5, 2005, now U.S.Pat. No. 7,629,015 issued Dec. 8, 2009 which is a divisional applicationunder 35 U.S.C. §120 of U.S. Pat. application Ser. No. 10/399,845, filedSept. 26, 2003 (acceptance date), now U.S. Pat. 7,625,617, issued Dec.1, 2009, which is a U.S. National Stage application under U.S.C. §371 ofInternationals Application No. PCT/AU01/01339, filed Oct. 19, 2001,which claims priority to Australian Provisional Patent Application No.PR903, filed Oct. 20, 2000. Each of the foregoing disclosures is hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to medical electrical leads and electrodesand, in particular, to medical leads having electrodes made from ametal-coated polymeric material.

BACKGROUND ART

Electrical leads and electrodes are commonly utilized in the medicalfield for applications such as stimulation, sensing, ablation anddefibrillation.

Traditionally, medical electrodes comprise machined metal or coiledmetal wire components, which, while suitably conductive, do not providethe flexibility in both design and mechanical properties afforded by ametal-coated polymer. Furthermore, metal-coated polymers areparticularly suitable for use in larger area electrodes where theirlightweight, flexibility and versatility are key advantages.

The use of metal-coated or metal-filled polymers as medical electrodeshas been considered. For example, in U.S. Pat. No. 5,279,781, ametal-filled fiber for use as a defibrillation electrode is described.The metal in this case is added during the spinning process. To renderthe electrode suitably conductive, however, requires the addition of asignificant proportion of metal to the fiber, which, in turn, has anadverse effect on the mechanical strength of the electrode.

Further structures, including metal-filled silicones and intrinsicallyconductive polymers, have been considered for use as medical electrodesalthough it has been found that such structures do not have the requiredlevel of conductivity necessary for the abovementioned medicalapplications.

Typically, the problem encountered with using a polymeric material as anelectrode is that it is difficult to obtain a good electrical connectionto the electrode. In U.S. Pat. No. 5,609,622, an electrical connectionwas achieved by utilizing an electrode having metal wires embedded inits wall. The electrode was then subjected to an ion beam treatment withmetal, such that the metal was deposited within the wall and, therefore,contacted the wires. In this case, however, the electrical connectionwas only shown to occur at one end of the electrode and further, it isquestionable whether a good connection is achieved by this method as itrelies upon the incidence of metal contacting wire through the thicknessof polymeric material.

The present invention provides an electrical lead and/or electrode thatovercomes the problems of the prior art.

Any discussion of documents, acts, materials, devices, articles, or thelike, which has been included in the present specification, is solelyfor the purpose of providing a context for the present invention. It isnot to be taken as an admission that any or all of these matters formpart of the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

DISCLOSURE OF THE INVENTION

Throughout this specification, the word “comprise,” or variations suchas “comprises” or “comprising, ” will be understood to imply theinclusion of a stated element, integer or step, or group of elements,integers or steps, but not the exclusion of any other element, integeror step, or group of elements, integers or steps.

According to a first aspect, the present invention may include anelectrically conductive member including an elongate body, the bodyhaving at least one electrically conductive region, the regioncomprising a porous polymeric material coated with an electricallyconductive material.

Preferably, the electrically conductive member is adapted for medicaluse and, in particular, but not limited to, use in cardiac mapping,defibrillation or pacing, neurological applications including neuralstimulation implants, muscle stimulation, sensing and ablation.Accordingly, in a preferred embodiment, the electrically conductivemember may comprise part of a lead or any other form of carrier.

Typically, the electrically conductive member is an elongate tube. Whilethe entire length of the member may be made from a porous polymer coatedwith an electrically conductive material, it is also envisaged that theelectrically conductive member may comprise a plurality of distinctelectrically conductive regions made up of the coated porous polymer.

In the embodiment wherein the electrically conductive member is tubular,it is preferred that the pores of the at least one electricallyconductive region are present substantially across the diameter of asidewall of the tubular structure. Accordingly, in this embodiment,electrical connection may be made from internal a lumen of the tube. Itis further envisaged that electrical connection may be made from withinthe sidewall of the tube as further discussed below.

Rather than a tube, the electrically conductive member may comprise asolid cylindrical member. In this embodiment, it is again preferred thatthe pores of the at least one electrically conductive region are presentsubstantially across the diameter of the cylindrical member.

In a preferred embodiment, the pores of the polymeric material of the atleast one electrically conductive region are greater than 5 microns andpreferably between 30 microns and 100 microns. When the porous polymericmaterial is coated with an electrically conductive material, theelectrically conductive material preferably coats and lines at leastsome of, and preferably all of, the pores.

Typically, the electrically conductive material is a metal and,preferably, a biocompatible metal such as platinum. It is envisaged,however, that a combination of two or more metals or metal alloys may beused to improve electrical conductivity. For example, it may bedesirable to provide a first layer of copper or silver or any othersuitably conductive metal and a second layer of platinum to enable useof the electrically conductive member within a body.

The coating of the porous polymeric material preferably creates asuitably thick layer of metal coating across the at least oneelectrically conductive region. Preferably, the resistance of thecoating is less than 100 ohms and more preferably less than 10 ohms.

The porous polymeric material may be expanded polytetrafluoroethylene(PTFE), wherein the pore size is adjusted to allow the metal coating topenetrate the pores and to produce a coating of sufficient thickness toprovide adequate electrical conductivity. Other materials are envisagedincluding, but not limited to, porous silicones, porous polyurethanes,polyether block amide (PEBAX) or nylon. In each case, the pore size maybe varied depending upon the method of formation of the porous materialor by the addition of additives such as sodium chloride (NaCl), sodiumbicarbonate (Na₂HCO₃) or polyglycolide, which can be leached outfollowing molding or extrusion, leaving a porous structure.

Alternatively, the pores of the polymeric material may be formed bydrilling into the polymer using a laser drill. This has the particularadvantage of enabling only a portion of the polymer to be of a porousnature.

The at least one electrically conductive region may be electricallyconnected to an electrical conductor.

In one embodiment, the electrical conductor is a straight or coiledwire, or number of wires, embedded within the body of the electricallyconductive member and preferably within the at least one electricallyconductive region of the member. If the electrically conductive memberis a solid cylindrical member, the wire or wires may be coiled in ahelical manner within the at least one electrically conductive region.If the electrically conductive member is a tubular structure, the wireor wires may be coiled in a helical manner within the wall of the tubeand preferably within the at least one electrically conductive region.In either embodiment, the wire(s) may extend through several pores ofthe at least one electrically conductive region. Accordingly, when theporous polymeric material of the at least one region is coated with theelectrically conductive material, the portions of wire that extendthrough the pores may be simultaneously coated with the electricallyconductive material, thereby creating a good electrical connectionbetween the electrical conductor and the electrically conductive region.

The wires may be single wires or multifilament wires. Further, the wireor wires may be made of copper, preferably coated with a noble metal,such as palladium or platinum, for corrosion resistance. Alternatively,the individual wires may be a multifilament stainless steel wire. Othersuitable materials include, but are not limited to, platinum or platinumalloy, MP35N or ELGILOY®.

In the above embodiment, depending upon the application of theelectrically conductive member, the wire(s) may be connected by aninsulated conductor to either a source of electricity or to an analyzermeans. Typically, the wire(s) are connected to the insulated conductorby way of welding. Alternatively, they may be connected by electricallyconductive adhesives or by soldering.

In a further embodiment, the electrical conductor is located internalthe elongate body of the electrically conductive member. For example, ifthe electrically conductive member is a tube having at least oneelectrically conductive region, the electrical conductor may bepositioned within the lumen of the tube. In this embodiment, theelectrical conductor is preferably adapted such that it engages theinternal surface of the tube. To ensure that the electrical conductorengages the tube, it is preferred that the electrical conductorcomprises a resilient spring, such as a spiral spring, that, oncepositioned in the tube, can expand into contact with the inner wall ofthe tube.

In another embodiment, the electrical conductor may be a spring formedfrom a shape memory alloy such as Nitinol. The shape memory springpreferably moves, when exposed to a pre-determined temperature, from afirst position to a second position, wherein, when in the secondposition, the spring expands such that it has an outer diameter greaterthan the inner diameter of the tube. Accordingly, when internal thelumen of the tube and when in the expanded second position, the springengages the inner surface of the tube to a sufficient extent to providea good electrical connection between the electrical conductor and the atleast one electrically conductive region.

In one embodiment, the shape memory alloy spring expands into contactwith the inner surface of the tube upon exposure to body temperature.

The shape memory spring may be connected to an insulated conductor bywelding, the use of electrically conductive adhesives or soldering.

In the above embodiments, it is preferred that the electrical conductorsuch as the wire(s) embedded within the electrically conductive memberor a shape memory alloy spring positioned within a lumen of a tubularelectrically conductive member, extends the entire length of theelectrically conductive member, or at least the length of the at leastone electrically conductive region, such that a good electricalconnection between the electrical conductor and the at least oneelectrically conductive region can be made.

In another embodiment, the electrical conductor is adapted to engage anend of the electrically conductive member. For example, the electricalconductor may include a shape memory alloy tube that is adapted toexpand and increase its internal diameter upon heating above apre-determined temperature or exposure to a particular pre-determinedtemperature. The shape memory alloy tube may then be slid over an end ofthe electrically conductive member. Upon heating above or cooling belowthe pre-determined temperature depending on the type of shape memoryalloy, the shape memory alloy tube preferably returns to its originalunexpanded shape, therefore, effectively clamping down on an end of theelectrically conductive member. This embodiment provides a uniformradial pressure on the end of the member and provides a good electricalconnection between the electrical conductor and the at least oneelectrically conductive region of the member. If the electricallyconductive member is a tube, it may be necessary to provide an innertube which is relatively stiff and which may be positioned internal thelumen of the tube to prevent collapse of the member.

In a second aspect, the present invention may include a method ofmanufacturing the electrically conductive member of the first aspect,the method comprising the steps of:

(i) extruding an elongate body of polymeric material, wherein at leastone region of the elongate body is porous in nature; and

(ii) coating the elongate body with an electrically conductive materialsuch that the electrically conductive material substantially coats thepores of the at least one region.

While the entire length of the elongate body may be coated with theelectrically conductive material, in the embodiment wherein there aredistinct regions of porous polymeric material, it may be preferred thatonly the distinct porous regions are coated with the electricallyconductive material rather than the entire length of the elongate body,which may include non-porous regions.

Where the electrical conductor comprises a straight or coiled wire, theelectrically conductive member may be manufactured in a number ofstages. For example, a first tube, or layer, or solid cylindrical membermay be formed from either a porous polymeric material or non-porouspolymeric material or a combination thereof. The wire may then bewrapped around and along at least a portion of the first tube or solidcylindrical member in a helical manner or extended along at least aportion of the length of the first tube or layer or solid cylindricalmember. The wire and the first tube or layer or solid cylindrical membermay then be overlaid with a coating or another layer. The coating or theother layer may be a porous polymeric material or, alternatively, apolymeric material having regions that are of a porous nature. In oneembodiment, the coating may be a second tube.

In a further embodiment of the second aspect, the electricallyconductive member may comprise a tube. In this embodiment, theelectrical conductor is positioned within the lumen of the tube. Theelectrical conductor is preferably positioned such that it engages theinternal surface of the tube. To ensure that the electrical conductorengages the tube, it is preferred that the electrical conductorcomprises a resilient spring, such as a spiral spring that, oncepositioned in the tube, can expand into contact with the inner wall ofthe tube.

In another embodiment of the second aspect, the electrical conductor canbe formed in a spring form from a shape memory alloy such as Nitinol.The shape memory spring can preferably move from a first position to asecond position, wherein, when in the second position, the spring couldexpand such that it had an outer diameter greater than the innerdiameter of the tube.

The electrical conductor may be adapted to engage an end of theelectrically conductive member. For example, the electrical conductormay include a shape memory alloy tube that is adapted to expand andincrease its internal diameter upon heating above a pre-determinedtemperature. The shape memory alloy tube may then be slid over an end ofthe electrically conductive member. Upon heating above or cooling belowthe pre-determined temperature depending on the type of shape memoryalloy, the shape memory alloy tube preferably returns to its originalunexpanded shape, therefore effectively clamping down on an end of theelectrically conductive member. This embodiment provides a uniformradial pressure on the end of the electrically conductive member andprovides a good electrical connection between the electrical conductorand the at least one electrically conductive region of the member.

Typically, the electrically conductive material is applied to theelongate body or preferably to the at least one electrically conductiveregion using a wet technique such as electroless plating. In thisembodiment, the electrically conductive material may be forced throughthe pores of the at least one electrically conductive region by theapplication of pressure.

Alternatively, the electrically conductive material may be applied byelectroless plating followed by the additional step of electroplating.

Each of the above processes preferably ensures that a coating ofelectrically conductive material penetrates substantially all the poresof the electrode. If the at least one region of electrically conductivematerial has pores disposed substantially throughout the entirethickness of the region, it is envisaged that electrical connection maybe made by way of an electrical conductor, as described above, eitherwithin the wall of the elongate body or on the inside of the elongatebody (for example, if the elongate body is a tubular structure).

The process of coating the elongate body with an electrically conductivematerial such that the pores of the at least one electrically conductiveregion are coated with such a material may involve a number of stepsprior to the actual coating with the electrically conductive material.The steps include:

(1) Cleaning.

(2) Surface Modification.

(3) Catalysis.

(4) Coating.

-   (1) The material to be coated is typically washed in an organic    solvent, such as acetone or ethyl acetate, or in a solution    containing a suitable surface active agent. Usually some agitation    is required, such as from an ultrasonic cleaner or a shaker water    bath. The step of cleaning may be carried out above room    temperature.-   (2) The step of surface modification results in a more wettable or    hydrophilic surface, such that the deposition of the coating may be    accelerated and, further, chemical and mechanical adhesion of the    coating to the surface may be improved.

Chemical adhesion may be improved by creating the most suitablefunctional groups on the surface of the polymer such as amides, whilemechanical adhesion may be improved by creating a roughened surfaceusing chemical (etching) or mechanical (sandblasting) methods.

Typically, the surface modification chemicals are infused into the poresusing pressure via a pump or syringe. Alternatively, the porous materialto be coated may be placed in the treatment solution and evacuated in avacuum, thereby removing gas bubbles from within the porous structureresulting in contact of all surfaces with the treatment solution.

Additionally, plasma treatment may be used to improve wettability and/orimprove chemical or mechanical adhesion.

Following this step, the structure to be coated is rinsed several times,preferably in deionized water.

-   (3) The catalyst step results in the deposition of a small amount of    noble metal on the surface of the material. This provides the sites    for deposition of the coating material, for example, platinum. While    typical electroless plating uses a tin/palladium catalyst, it is    preferred that a process that eliminates the tin is used. For    example, palladium in an acidic aqueous solution or dimethyl    sulfoxide, both of which can be reduced in a hydrazine solution, is    preferred. The latter is particularly useful as, being an organic    solution, it allows improved wettability for many substrates.

In one embodiment of the catalysis of a material such as silicone, thecatalyst, in the form of palladium metal powder, can be mixed into asilicone dispersed in a solvent and then infused into the pores andcured prior to coating. In this embodiment, a small concentration ofactual silicone is required so as to provide a thin layer on the surfaceof the pores rather than fill the pores with silicone. The palladiummetal will act as a catalyst and will be bound to the silicone and,therefore, increase the adhesion of the coating material that issubsequently applied.

Alternatively, the silicone mix may be infused with palladium prior tomolding or extrusion.

The catalyst step may be performed a number of times.

-   (4) The coating process preferably uses electroless plating, wherein    a number of metals may be deposited using either commercially    available or custom made solutions of complex metal ions, together    with a stabilizer and an added reducer. The solution typically    allows controlled deposition of a metal over a specific period of    time. If a biocompatible electrode is required, it is preferred that    the metal is platinum.

A fifth step may be added to the above process if a thicker coating ofmetal and, therefore, higher conductivity is required. This wouldinvolve further electroless plating or electroplating.

In a further embodiment, following the process of coating, the pores areinfused with a liquid adhesive such as, but not limited to, a siliconedispersant to effectively seal the pores. Preferably, the infusion ofthe adhesive is carried out from within the electrically conductivemember when the member is a tubular structure. This embodiment has theadvantage of enabling an electrically conductive member to be implantedin a body for long periods of time with minimal tissue ingrowth into themember. This facilitates easy removal of the member if required.

In a third aspect, the present invention may include an electricallyconductive member including an elongate body, the elongate body havingat least one electrically conductive region comprising a polymericmaterial, together with at least one electrical conductor wherein atleast a portion of the polymeric material and at least a portion of theat least one electrical conductor have a coating thereon of anelectrically conductive material.

Preferably, the elongate body comprises a tubular body made of asuitable polymer material. The electrical conductor is preferably housedwithin at least part of a side wall of the tubular body. In addition tobeing housed within a side wall of the tubular body at the at least oneelectrically conductive region of the body, the electrical conductor mayextend along the entire length of the tubular body.

The elongate body preferably comprises a first cylindrical inner memberand a second outer member, the second outer member substantially forminga coating around the first inner member. The second outer memberpreferably extends over the entire length of the first inner member. Theat least one electrical conductor is preferably sandwiched between thefirst inner member and the second outer member.

The first inner member may be made from a suitable polymeric materialsuch as polyurethane, polyether block amide (PEBAX), PEEK or polyimide.The second outer member is preferably formed from a similar polymericmaterial to that of the first inner member. Further, it is preferredthat the second outer member is made from a transparent, or at leastsubstantially transparent, material such that the at least oneelectrical conductor may be viewed through the second outer member.

Preferably, the second outer member is much thinner than the first innermember and typically, the second outer member is sufficiently thick toonly just cover the at least one electrical conductor.

The at least one electrical conductor may comprise a metal wire or wiresmade from material such as PFA, polyimide insulated copper wire(s) orcopper alloy wire(s). Preferably, the wire(s) have a diameter ofapproximately 0.025 mm to 0.3 mm.

Typically, during manufacture, single wires may be wound substantiallyaround the circumference of the first inner member. Preferably, between8 to 24 wires are wound around the first inner member in this manner,wherein each wire has a predetermined spacing between it and the nextwire. These 8 to 24 wires may form a particular group that is spacedfrom a second or subsequent group of wires by a gap, which is preferablylarger than the gap between each wire of each group. In this way,identification of each group may be more easily determined. To aididentification, each group may further be color coded.

The at least one electrical conductor may be helically wound around thefirst inner member. However, the present invention is not limited to theparticular arrangement of the at least one electrical conductor and anumber of combinations and orientations are envisaged.

Preferably, at least one portion of the at least one electricalconductor is not overlaid by the second outer member, that is, the atleast one portion is exposed to the outside environment. The at leastone portion of the electrical conductor of this embodiment is preferablycoated with the electrically conductive material. It is furtherpreferred that at least a portion of the polymeric elongate bodyadjacent the exposed portion of the electrical conductor is also coatedwith the electrically conductive material.

Typically, a band around the circumference of the elongate body iscoated, together with the exposed portion of the electrical conductor,to form a band electrode on the elongate body.

Preferably, the electrically conductive material is a metal and,preferably, a biocompatible metal such as platinum. It is envisaged thata combination of two or more metals or metal alloys may be used,however, to improve electrical conductivity. For example, it may bedesirable to provide a first layer of copper or silver or any othersuitably conductive metal and a second layer of platinum to enable useof the electrically conductive member within a body.

It is preferred that the exposed at least one portion of the electricalconductor is protected from corrosion. This may be achieved by, forexample, immersing the elongate body in a solution such as palladiumchloride, which will coat the exposed portion(s).

In a fourth aspect, the present invention provides a method ofmanufacturing an electrically conductive member, the method comprisingthe steps of:

(i) extruding an elongate inner member from a polymeric material;

(ii) applying at least one electrical conductor to an exposed surface ofthe inner member;

(iii) overlaying the inner member and the at least one electricalconductor with an outer member made from a polymeric material, such thatthe at least one electrical conductor is covered by the outer member;

(iv) exposing at least a portion of the at least one electricalconductor; and

(v) coating the exposed portion of the at least one electrical conductorand at least a portion of the outer member with an electricallyconductive material.

Preferably, the inner member is extruded as a tube made from a suitablematerial such as polyurethane or polyether block amide (PEBAX).

The at least one portion of the at least one electrical conductor may beexposed by a number of means including, but not limited to, applyingheat, chemicals or lasers to remove the area of the outer layer coveringthe at least one portion. Desirably, a laser technique is used (e.g.,quadruple Yag laser) as such a technique provides good accuracy. Forexample, the laser beam is capable of following a particular path of,say, a helically wound wire acting as the at least one electricalconductor. While only a small portion of the at least one electricalconductor may be exposed in this manner, the present invention is notlimited to the amount of electrical conductor exposed and, indeed, theentire electrical conductor may be exposed.

For high energy applications, such as radio frequency (RF) or microwaveablation, adjacent electrical conductors may be exposed and coated withelectrically conductive material to form a single electrode. Such aconfiguration decreases the current density. The electrical conductorsof this embodiment may be electrically connected to each other at aproximal end of each electrical conductor. The number of electrodesformed together with the spacing between each electrode may be varied.

The exposed portion of electrical conductor(s) may be protected fromcorrosion by immersion in an acidic solution of, for example, palladiumchloride, which will coat all the exposed portions.

It is desirable that the at least one portion of the at least oneelectrical conductor and at least a portion of the elongate body, whichtogether are coated to form an electrode, are catalyzed. To preventcatalysis of the remainder of the elongate body or electrical conductorthat form a non-electrode area, these areas are protected from catalysisby masking them by, for example, photolithography or by using pieces ofheat shrink tubing such as PET to protect the areas. An alternative tomasking is the use of an ink that is pad printed over the areas to becoated and, thus, the areas that are to become the electrodes. The inkused may or may not be electrically conductive but, in any event, shouldbe able to catalyze a subsequent plating step. If radio opacity isrequired, it may be desirable to use an ink including colloidalpalladium or silver.

The catalyst step results in the deposition of a small amount of noblemetal on the surface of the material to be coated. This provides thesites for deposition of the electrically conductive material, forexample, platinum. While typical electroless plating uses atin/palladium catalyst, it is preferred that a process that eliminatesthe tin is used. For example, palladium in an acidic aqueous solution ordimethyl sulfoxide, both of which can be reduced in a hydrazinesolution, is preferred. The latter is particularly useful as, being anorganic solution, it allows improved wettability for many substrates.

The catalyst step may be performed a number of times.

The coating process preferably uses electroless plating, wherein anumber of metals may be deposited using either commercially available orcustom made solutions of complex metal ions, together with a stabilizerand an added reducer. The solution typically allows controlleddeposition of a metal over a specific period of time. If a biocompatibleelectrode is required, it is preferred that the metal is platinum.

If relatively thick coatings are required, it is preferred that a porouspolymer is used.

The electrodes formed with respect to the third and fourth embodimentsmay be protected by a layer of, for example, polyethylene glycol ormannitol. Such a protective layer preferably allows an electrical chargeto pass therethrough.

The following examples describe the preparation of the electrodeaccording to several embodiments of the first and second aspects of thepresent invention.

EXAMPLE 1

A porous polyurethane tube was made using a spraying system. First, awire mandrel was connected to an electrical motor using a chuck. Thewire was simultaneously coated with a mixture of polyurethane(PELLETHANE®) dissolved in dimethylformamide (1% polyurethane) andwater. The water polymerized the polyurethane prior to deposition,creating a porous layer. A copper wire was then wound onto the coatedmandrel and a further layer was uniformly coated with the mixture ofpolyurethane dissolved in dimethylformamide and water. The sprayingcontinued until the appropriate diameter was achieved, i.e., 2.2 mm(this was chosen as once assembled into a lead, a 2.2 mm lead body wouldcomfortably pass down a 7 French introducer).

The porous component was then coated with platinum using the normalcleaning, surface modification, catalysis and coating steps previouslyoutlined.

The resistance was then measured to be approximately 0.5Ω for a 1 cmlength of the porous component, and approximately 1Ω from the end of thecopper wire to the surface of the component.

EXAMPLE 2

An expanded PTFE tube was supplied by Impra, which had a pore size of 30microns. The tube was immersed in alcohol and placed in an ultrasoniccleaner to remove air bubbles and wet the surface.

The sample was removed from the alcohol and etched for 1 minute withFLUOROETCH® from Acton Technologies, Inc., Pittson, PA. A syringe wasused to try and force the solution through the pores; however, this wasunsuccessful.

The tube was then catalyzed using a 2 g/l solution of PdCl₂ in DimethylSulfoxide for 5 minutes, intermittently attempting to force thesolutions through the pores. This was followed by a reduction step in 4%Hydrazine solution.

The catalyzed tube was then electrolessly coated using a platinumcomplex solution and hydrazine.

After 1.5 hours, the sample was a shiny, metallic color on the outside.

After drying, the resistance along the surface was found to beapproximately 20Ω for a 1 cm length; however, the resistance through thethickness varied from 25-50Ω.

EXAMPLE 3

Another expanded PTFE tube was supplied by Impra; however, this time,the pore size was increased to 90 microns. The tube was immersed inalcohol and placed in an ultrasonic cleaner to remove air bubbles andwet the surface.

The sample was removed from the alcohol and etched for 30 seconds withFLUOROETCH® from Acton Technologies, Inc., Pittson, PA. A syringe wasused to try and force the solution through the pores. This time, thesolution was able to freely pass through the structure.

The tube was then catalyzed using a 2 g/l solution of PdCl₂ in DimethylSulfoxide for 5 minutes, intermittently forcing the solutions throughthe pores. This was followed by a reduction step in 4% Hydrazinesolution.

The catalyzed tube was then electrolessly coated using a platinumcomplex solution and hydrazine, intermittently forcing the solutionthrough the pores.

After 1.5 hours, the sample was a shiny, metallic color on the outside.

After drying, the resistance along the surface was found to beapproximately 1.5Ω for a 1 cm length. The resistance through thethickness was approximately 1.5Ω. No materials were removed using astandard tape test to measure adhesion.

A 4 mm length was then cut and a 2.1 mm diameter Nitinol spring (fromMicrovena, White Bear Lake, Minnesota, USA) was straightened and passedup the middle of the cut platinum-coated tube. The structure was thenplaced in the oven at 70° C. and the Nitinol spring went back to itsoriginal shape clamping on the inside of the platinum-coated tube.

A length of 0.2 mm diameter copper wire was then welded to one end ofthe Nitinol spring. The resistance was found to be 1.8 ohms from the endof the copper wire and the outside of the platinum-coated expandedTEFLON®.

A PEBAX tube was passed over each end of the spring and then glued withepoxy forming a butt joint on each side of the platinum-coated expandedTEFLON® component.

After curing, the lead was then tested in an isolated cow heart, byimmersing the heart with an electrode attached into a conductive mediaand RF energy passed through the electrode to the heart, creatinglesions. The test device produced similar lesions to a commerciallyavailable ablation lead.

The same lead was tested when delivering pacing pulses and a suitableimpedance resulted.

Due to flexibility and versatility, the electrodes can be made differentshapes, sizes, numbers and spacing. This is important when designing newleads for various applications, e.g., ablation leads for treating atrialfibrillation.

The following examples describe the preparation of the electrodeaccording to several embodiments of the third and fourth aspects of thepresent invention.

EXAMPLE 4

A 1.6 mm diameter cable was sourced from MicroHelix, Inc., Portland,Oregon. The cable contained eight insulated wire coils in the wall ofthe tube. The insulating layer was made from a thin layer of PEBAX. Overone of the wires, a 4 mm length of insulation was removed to expose thecorresponding amount of wire. A 4 mm band of the cable around theexposed wire was masked. Some plateable conductive ink from CreativeMaterials Tyngsboro, MA was coated around the unmasked region coveringthe exposed conductor. The electrode with ink was then immersed in aplatinum complex electroless bath and coated for 1 hour at 60° C. usingHydrazine as the reducer resulting in a thickness of 0.5 micron. Thepacing impedance of the plated electrode was then measured in a 0.18%NaCl solution using a nickel plate as the return electrode. The pacingpulse used was 5 volts for 0.5 ms. The impedance was found to be 250ohms. This value was compared to a commercially available ablationelectrode, which was found to be 180 ohms. No damage to the coatedelectrode resulted.

EXAMPLE 5

A 1.6 mm diameter cable was sourced from MicroHelix, Inc., Portland,Oregon. The cable contained eight insulated wire coils in the wall ofthe tube. The insulating layer was a thin layer of PEBAX. Over one ofthe wires, a 4 mm length of insulation was removed to expose thecorresponding amount of wire. A 4 mm band of the cable around theexposed wire was masked. Some plateable conductive ink (CMI 117-31) fromCreative Materials Inc., Tyngsboro MA was coated around the unmaskedregion covering the exposed conductor. The electrode ink was coated witha 3 micron layer of copper using electroless plating. The copper-coatedelectrode was then immersed in an acid palladium chloride solution tocatalyze the surface and immersed again in platinum complex electrolessbath and coated for 1 hour at 60° C. using Hydrazine as the reducer. Thepacing impedance of the plated electrode was then measured in a 0.18%NaCl solution using a nickel plate as the return electrode. The pacingpulse used was 5 volts for 0.5 ms. The impedance was found to be 120ohms. This value was compared to a commercially available ablationelectrode, which was measured to be 180 ohms. No damage to the coatedelectrode resulted.

EXAMPLE 6

A 1.6 mm diameter cable was sourced from MicroHelix, Inc., Portland,Oregon. The cable contained eight insulated wire coils in the wall ofthe tube. The insulating layer was a thin layer of PEBAX. Over one ofthe wires, a 4 mm length of insulation was removed to expose thecorresponding amount of wire. A 4 mm band of the cable around theexposed wire was masked. Some plateable conductive ink (CMI 117-31) fromCreative Materials, Inc., Tyngsboro MA was coated around the unmaskedregion covering the exposed conductor. The electrode ink was coated witha 3 micron layer of copper using electroless plating. The copper-coatedelectrode was then immersed in an acid palladium chloride solution tocatalyze the surface and immersed again in platinum complex electrolessbath and coated for 1 hour at 60° C. using Hydrazine as the reducer.

The electrode was then placed on a piece of meat immersed in a 0.18%solution of NaCl and a stainless steel return electrode underneath.High-frequency RF power was delivered through the electrode for 60seconds, resulting in a lesion similar to a commercially availableablation electrode.

EXAMPLE 7

A 1.6 mm diameter cable was sourced from MicroHelix, Inc., Portland,Oregon. The cable contained eight insulated wire coils in the wall ofthe tube. The insulating layer was a thin layer of PEBAX. Over one ofthe wires, a 4 mm length of insulation was removed to expose thecorresponding amount of wire. A 4 mm band of the cable around theexposed wire was masked. Some plateable conductive ink (CMI 117-31) fromCreative Materials, Tyngsboro, MA was coated around the unmasked regioncovering the exposed conductor. The electrode ink was coated with a3-micron layer of copper using electroless plating. The copper-coatedelectrode was then immersed in an acid palladium chloride solution tocatalyze the surface and immersed again in platinum complex electrolessbath and coated for 1 hour at 60° C. using Hydrazine as the reducer.

The coated electrode was then immersed in a 0.18% NaCl solution using anickel plate as the return electrode. A biphasic defibrillation pulse130 volts in amplitude and 6 ms in pulse width was delivered through thecoated electrode, which resulted in no damage to the electrode and animpedance of 130 ohms.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are now described with referenceto the accompanying drawings, in which:

FIGS. 1 a, 1 b, and 1 c are side elevational views illustrating aconstruction of one embodiment of the present invention;

FIGS. 2 a, 2 b, and 2 c are cross-sectional views through I-I of FIGS. 1a, 1 b, and 1 c respectively;

FIG. 3 is a side elevational view of a cut-away portion of an embodimentof the invention;

FIGS. 4 a and 4 b are part cut-away, part side elevational views of afurther embodiment of the invention;

FIGS. 5 a and 5 b are side elevational views of a further embodiment ofthe invention;

FIG. 6 is a schematic view of a multi-electrode assembly incorporatingelectrically conductive regions of the present invention;

FIG. 7 is a perspective view of a number of electrically conductiveregions of the present invention in an electrode assembly;

FIGS. 8 a, 8 b, and 8 c are schematic views showing the steps ofmanufacture of an electrically conductive member according to a furtheraspect of the invention;

FIGS. 9 a, 9 b, and 9 c are schematic views showing the steps ofmanufacture of an electrically conductive member of another embodimentof the aspect depicted in FIGS. 8 a, 8 b, and 8 c; and

FIGS. 10 a, 10 b, and 10 c are schematic views showing the steps ofmanufacture of an electrically conductive member of a further embodimentof the aspect depicted in FIGS. 8 a, 8 b, and 8 c.

DETAILED DESCRIPTION

The lead 10 of the present invention includes an elongate body 11 havingat least one electrically conductive region 20 thereof made from aporous polymeric material. The porous polymeric material is coated withan electrically conductive material and preferably a metal such asplatinum.

As discussed above, the lead 10 of the present invention is adapted formedical use and, in particular, use in cardiac mapping, defibrillationor pacing, neurological applications including neural stimulationimplants, muscle stimulation, sensing and ablation.

As depicted in the drawings, the lead 10 has a tubular structure havinga wall 12 and an internal lumen 13. While only one region 20 of the tubemay be made from the porous polymeric material, it may be preferablethat the entire length of the tube is made from the material.

The pores within the wall 12 are preferably greater than 5 microns andpreferably between 30 microns and 100 microns.

The coating of the porous polymeric material with the metal creates asuitably thick layer of metal coating, thereby increasing electricalconductivity through the lead 10.

To establish a good electrical connection, the lead 10 includes aconductive member 14.

In one embodiment, depicted in FIGS. 1 a, 1 b, 1 c, the conductivemember 14 comprises a coiled wire 15 embedded within a wall 12 of thelead 10(FIG. 2 1 ). The wire 15 is wrapped around and along asubstantial length of the lead 10 and preferably along the entire lead.While not shown, the wire 15 may pass through several pores of thepolymeric material and, thus, when the porous polymer is coated with themetal, the portions of wire 15 within the pores may simultaneously becoated with the metal, thereby creating a good electrical connectionbetween the wire and the at least one electrically conductive region 20.

As shown in FIGS. 1 a, 1 b and 1 c, the lead of this embodiment may bemade in a number of stages. A first tube 16 is created as shown in FIG.1 a. The first tube 16 may, or may not be, porous in nature. The wire 15is subsequently wrapped around and along the first tube 16 in a helicalmanner and the wire 15 and first tube 16 subsequently overlayed with asecond porous polymer material 17(FIG. 3).

In another embodiment, the conductive member 14 is a shape memory alloyspring 18(FIGS. 4 1 and 4 b) such as a Nitinol spring. The spring 18 ofthis embodiment is positioned internal the lumen 13 of the lead 10. Inuse, the spring 18 may be exposed to a pre-determined temperature thatcauses it to expand such that it abuts with the internal surface 19 ofthe lead 10. Preferably, the spring 18 can normally expand to such anextent that its external diameter is greater than the diameter of thelumen 13 resulting in a good electrical connection between the springand the at least one electrically conductive region.

In another embodiment of the invention depicted in FIGS. 5 a and 5 b,the conductive member 14 is adapted to engage one end 21 of the lead 10.Preferably, the conductive member is a shape memory alloy tube 22, whichis adapted to expand and increase its internal diameter upon heatingabove or cooling below a pre-determined temperature depending on thetype of shape memory alloy. The shape memory alloy tube 22 may then beslid over the end 21 of the lead 10. Upon heating up or cooling belowthe pre-determined temperature depending on the type of shape memoryalloy, the shape memory alloy tube 22 returns to its original unexpandedshape, therefore, effectively clamping down on an end of the lead 10 asshown in FIG. 5 b. Accordingly, there is provided a uniform radialpressure on the end 21 of the lead 10, which results in a goodelectrical connection between the shape memory alloy tube 22 and the atleast one electrically conductive region. In this embodiment, it may benecessary to provide an inner, relatively stiff tube (not shown), whichmay be positioned internal the electrode 10 to prevent collapse of thelead 10.

Once the lead 10 has been coated with the selected metal, the lead 10may be cut to the desired length depending on the application of theelectrode. For example, a defibrillation electrode formed from the leadmay need to be a length of around 60 mm, whereas a lead acting as anelectrode for mapping or sensing need only be a few millimeters inlength.

A multi-electrode system along a lead may be constructed by threadingtogether lengths of coated tubes 23 or uncoated tubes 24 of specifiedlengths as depicted in FIG. 6. The coated tubes 23 and uncoated tubes 24are joined together using butt joints, which may have spring or tubingsupports (not shown) within the lumen of the respective coated anduncoated tubes 23 or 24.

In the aspect of the invention depicted in FIGS. 8 a, 8 b and 8 c, theinvention consists of an electrically conductive member 30 including anelongate body 31. The elongate body 31 has at least one electricallyconductive region 32, which comprises a polymeric material 33, togetherwith at least one electrical conductor 34. A portion of the polymericmaterial 33 and a portion or all of the electrical conductor 34 arecoated with an electrically conductive material 35.

The elongate body 31 comprises cylindrical first inner member 36 and asecond outer member 37, the second outer member 37 substantially forminga coating around the first inner member 36. The second outer member 37extends substantially over the entire length of the first inner member36. The at least one electrical conductor 34 is sandwiched between thefirst inner member 36 and the second outer member 37.

As shown in FIG. 8 b, the electrical conductor 34 is exposed. This maybe achieved by a number of means including the application of heat,chemicals or lasers to remove the area of the outer member 37 coveringthe electrical conductor 34.

The exposed electrical conductor 34 and an area of the polymericmaterial 33 adjacent the electrical conductor 34 is then catalyzed andcoated with the electrically conductive material 35 to form an electrode38.

As depicted in FIGS. 9 a, 9 b, and 9 c, two electrodes 38 may be formedby coating separate electrical conductors 34 together with an adjacentarea of polymeric material 33.

For high energy applications such as RF or microwave ablation, FIGS. 10a, 10 b and 10 c show how a number of electrical conductors 34, togetherwith their adjacent polymeric material 33, may be coated with anelectrically conductive material to form a single electrode 38. Theelectrical conductors 34 of this embodiment may be electricallyconnected to each other at a proximal end of each electrical conductor34. The number of electrodes 38 formed together with the spacing betweeneach electrode 38 may be varied.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. An electrical lead, including: an elongate body of a polymericmaterial, the elongate body comprising an inner member and an outermember arranged around the inner member; at least one electricalconductor positioned between the inner member and the outer member sothat the outer member overlies the at least one electrical conductor, atleast a portion of the at least one electrical conductor not beingoverlaid by the outer member; and a coating of an electricallyconductive material applied to an outer surface of the elongate body atleast in the region of the at least one portion of the at least oneelectrical conductor not overlaid by the outer member so that thecoating coats at least the at least one portion of the at least oneelectrical conductor to define at least one electrically conductiveregion on the elongate body.
 2. The electrical lead of claim 1, whereinthe coating also coats a part of the outer member surrounding the atleast one portion of the at least one electrical conductor not overlaidby the outer member.
 3. The electrical lead of claim 1, wherein theelongate body is tubular and wherein the at lease one electricalconductor is contained within at least part of a wall of the tubularelongate body.
 4. The electrical lead of claim 1, further including aplurality of electrical conductors wound helically about the innermember.
 5. The electrical lead of claim 1, wherein the inner member andthe outer member are made from a polymeric material selected from thegroup consisting of polyurethane and polyether block amide (PEBAX). 6.The electrical lead of claim 1, wherein the outer member is transparentso that the at least one conductor is visible through the outer member.7. The electrical lead of claim 1, wherein the coating comprises a firstlayer overlain by a second layer of a biocompatible material.
 8. Theelectrical lead of claim 7, wherein the first layer is catalyzed.
 9. Theelectrical lead of claim 1, wherein the coating forms a band electrodeextending substantially around a periphery of the elongate body.